The petroleum industry is increasingly turning to heavy crudes, resids, coals and tar sands as sources for feedstocks. Feedstocks derived from these heavy materials contain more sulfur and nitrogen than feedstocks derived from more conventional crude oils, requiring a considerable amount of upgrading in order to obtain usable products therefrom. The upgrading or refining generally being accomplished by hydrotreating processes, i.e., treating with hydrogen of various hydrocarbon fractions, or whole heavy feeds, or feedstocks, in the presence of hydrotreating catalysts to effect conversion of at least a portion of the feeds, or feedstocks to lower molecular weight hydrocarbons, or to effect the removal of unwanted components, or compounds, or their conversion to innocuous or less undesirable compounds.
Catalyst precursors commonly used for these hydrotreating reactions include materials such as cobalt molybdate on alumina, nickel on alumina, cobalt molybdate promoted with nickel, nickel tungstate, etc. U.S. Pat. Nos. 4,824,821 and 5,484,755 and US Patent Publication No. 2006/0054535 disclose hydroprocessing catalysts in the form of high activity slurry. The slurry catalyst is produced from group VIB metal compounds by sulfiding an aqueous mixture of the metal compound with hydrogen sulfide (H2S) gas at a pressure of up to 5,000 psi (340 atm).
US Patent Publication No. 20070161505 discloses an ultra-dispersed catalyst composition having a median particle diameter between 30-6000 nm, prepared by mixing separate micro-emulsions of Group VIB or VIIIB non-noble metals. Each micro-emulsion is prepared by mixing solutions containing either Group VIB or VIIIB metal with a hydrocarbon feedstock. As the metals were sulfided separately, when the micro-emulsions are mixed together, a first metal component (e.g., NiS) simply deposits on the outer layer of the second metal component (e.g., MoS2), thus forming a “core shell” type catalyst structure. Core-shell type catalysts formed with pre-sulfided metal components have lower catalytic activity than catalysts formed in a process wherein the metals are allowed to react/in contact with each other prior to sulfidation to form a more homogeneous structure.
In the preparation of a bulk slurry type catalyst, it is desirable to increase the incorporation of sulfur in the catalyst precursor in the sulfidation step.
The invention relates to an improved process to prepare bulk catalysts for use in the conversion of heavy oils and residua, wherein sulfur additives are used.